1. Field of Invention
The present invention relates in general to a method and apparatus for chemical vapor deposition (CVD), and more particularly to a method and apparatus for CVD that prevents contamination and enhancing film growth rate by directing a reactive gas for forming a film to the midst of a reaction chamber, and concentrating the reactive gas diffused over a susceptor in the chamber to prevent the reactive gas from being touching components of the reaction chamber.
2. Description of the Related Art
Chemical vapor deposition (CVD) is a thin film deposition process for forming solid material over the surface of a substrate using a reactant (usually in the form of gas, i.e., a reactive gas). As depicted in FIG. 1, a conventional apparatus for CVD comprises in general a reaction chamber 3 producing a vacuum, an inlet 7 for supplying the reactive gas to the chamber 3, a heating means 44 for chemically reacting the reactive gas supplied, outlets 6 for discharging exhaust gas, and a susceptor 5, located in the midst of the chamber 3, on which a substrate 55 is placed and the deposition occurs. When a given composition of vapor phase, including a main source material that participates directly in forming films and an auxiliary source material for carrying, vaporizing or diluting the main source material, is injected into the vacuum chamber 3, the composition is diffused instantly in all directions, such that the density of the reactive gas may have finite value at all over the inside of the reaction chamber. Especially, a portion of the composition in the vicinity of the susceptor is excited by hot temperature of the susceptor to form films on the substrate.
The conventional CVD apparatus is mainly used for making thin films less than 3 μm in thickness due to a low growth rate. To form a thick film more than 3 μm in thickness, it is necessary to increase the density of the reactive gas in the chamber considerably. However, the reactive gas injected into the chamber 3 generates undesired films or powders on the reaction chamber components such as walls, reactive gas distributing showerheads, substrate heating devices, inspection windows, etc. Moreover, the undesired films and/or powders formed on the reaction chamber components are broken to be small particles by repeated thermal expansion/contraction and/or lattice parameter mismatch between the reaction chamber components, thus contaminating the thin films while manufacturing. Here, if the number of the contaminant particles in the chamber 3 is increased, the reliability of the manufacturing process is deteriorated seriously. For example, in case of making very large scale integration (VLSI), the contaminant particles result in serious pattern inferiority such as circuit short.
Meanwhile, to enhance film growth rates in the conventional CVD system, it is necessary to increase the density of the reactive gas in the vicinity of the susceptor by adding the reactive gas to all space of the chamber 3 in practice, which requires the amount of the reactive gas excessively, thus deteriorating the economic efficiency.
To prevent contamination and undesired deposits in the reaction chamber 3, it may be considered to regulate the chamber temperature appropriately. However, the range of the temperature regulatable is very narrow, and furthermore, if the reactive gas is composed of several source materials, the range of temperature to regulate doesn't exist actually. Consequently, it is impossible to prevent generation of contaminant particles by regulating the reaction chamber temperature.
Besides, in the conventional CVD system, the temperature difference between the inner wall of the chamber 3 and the susceptor 5 causes a natural convection, which makes it difficult to maintain the diffusion of the reactive gas uniformly onto the substrates, thus deteriorating the reliability of the films formed. Moreover, the natural convection makes the contaminant particles generated continue to re-circulate in the chamber, which aggravates the problem of the contamination.
Accordingly, to manufacture a thick film more than 3 μm in thickness or VLSI circuits rapidly and economically, it is required to provide an improved method and apparatus for CVD that can prevent contamination, even when highly concentrated reactive gas is injected into the reaction chamber, and increase the density of the reactive gas in the vicinity of the susceptor in the reaction chamber considerably without raising the amount of the reactive gas supplied.
Following two conventional methods relate to the methods for increasing the density of the reactive gas in the vicinity of the susceptor in the chamber 3, and preventing generation of contaminant particles, respectively, which are considered as prior arts of the present invention.
First, as depicted in FIG. 2, U.S. Pat. No. 5,851,589 describes a CVD apparatus including a first gas, containing a reactive gas, fed in parallel to the surface of the substrate 55 through a pipe 2, and a second gas, containing a purge gas (non-reactive-gas), blown perpendicularly towards the surface of the substrate 55 through a injecting plate 1 to stabilize and make laminar flowing state of the first gas. Next, referring to FIG. 3, U.S. Pat. No. 6,301,434 discloses a dual gas manifold providing purge gas through a top showerhead 6 to prevent deposits on the window 8 and providing reactive gas through a lower showerhead 7 to deposit films on the substrate 55. The prior arts described above positively employed the control of purge gas to relax the conventional contamination problem. However, it seems that relaxation of the contamination is done only at the limited portion of the whole reaction chamber in both prior arts cited.
In FIG. 2, there exists an unavoidable re-circulation zone near the leading edge of the substrate, and it is difficult to suppress the diffusion of the reactive gas to the chamber wall, which deteriorates the effectiveness of the reference system. Moreover, the external control of purge gas flow rate may need much trial to make the reactive gas flow stabilized, since the laminar flow zone of the reactive gas is very narrow while the purge gas suppresses the narrow zone overall perpendicularly, thereby involving the latent instability of the flow. In FIG. 3, although the purge gas control system may be effective in preventing deposits on the window of the lamp system, it is not sure whether the reference apparatus could prevent particles being formed on the surface of the reaction chamber components such as chamber walls, especially around the areas far away from the purge gas showerhead. This problem would become serious when long process time and/or high growth rate is required.
Accordingly, the present invention is invented to provide a method and apparatus for chemical vapor deposition, which eliminates the drawbacks of the above-mentioned prior art. That is, the method and apparatus for CVD can form efficiently thick films more than 3 μm in thickness of high quality with excellent reproducibility, uniformity, controllability, and high growth rate using a protective curtain formed by a mutual diffusion-suppressing action between the purge gas and reactive gas.